1. Field of the Invention
The present invention relates to a polishing composition for selectively polishing a metal film on a semiconductor wafer and a polishing method of using the composition.
2. Description of the Related Art
A typical semiconductor wafer comprises a substrate such as a silicon or gallium arsenide wafer, and a plurality of integrated circuits are formed on the substrate. The integrated circuits are chemically or physically integrated on the substrate by patterning the regions in the substrate and layers on the substrate. The layers are generally formed of a material having any one of a conductivity, an insulating property and a semiconducting property. In order to obtain semiconductor devices at a high yield, it is very important to start from a flat semiconductor wafer. To this purpose, the surface or a certain part of the semiconductor wafer must be often polished.
According to the surface formation by conventional techniques, the upper surface of the wafer is disadvantageously left to have a topography still in a very irregular state such that upheavals, uneven height regions, troughs, trenches and other similar surface irregularities are present. Therefore, the surface must be planalized overall so as to ensure a sufficiently large depth of focus in photolithography and to remove the irregularity and surface defects during various steps in the production process. For attaining flatness on the wafer surface, several polishing methods are known and a chemical/mechanical planalization or polishing (CMP) is used over a wide range in the treatment for rendering the wafer surface flat during various steps in the production of a device, so that the yield, performance and reliability can be improved.
The slurry used for this chemical/mechanical polishing is formed from an acidic or basic solution containing abrasive grains such as silica, alumina, zirconia, ceria or titania.
The CMP technique is essential in the production process of a semiconductor device, particularly in the planalization of an interlayer insulating film for the formation of a multi-layer interconnection, in the formation of a conductive plug which is a metal, or in the formation of flush wiring.
With respect to the slurry for CMP used in the formation of a conductive plug which is a metal film comprising tungsten, aluminum, copper, titanium or an alloy thereof, JP-A-8-83780 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent application (Kokai)xe2x80x9d) discloses an abrasive composition containing a polishing accelerator such as an aminoacetic acid and/or amidosulfuric acid or an oxidizing agent, and a chemical reagent such as benzotriazole, and JP-A-8-197414 discloses a slurry containing a metal oxide particle such as fumed silica or fumed alumina having specific properties.
Conventional slurries for polishing a metal film of a semiconductor device are disadvantageous in that both the polishing rate for a metal film and the ratio (selection ratio) of the polishing rate for a metal film to the polishing rate for an oxide film (insulting layer) such as silica cannot be increased or, even if the polishing rate is high, a large number of scratches are generated on the polished surface.
The object of the present invention is to provide a slurry composition for polishing a metal film on a semiconductor substrate, which ensures a high polishing rate for a metal film, a high selection ratio, and reduction in the generation of scratches on the polished surface, as well as a method for polishing using the above composition.
As a result of extensive studies to achieve the above-described object, the present inventor has made the present invention.
More specifically, the present invention provides a slurry composition for polishing a metal film on a semiconductor substrate, comprising alumina-type fine particles containing or not containing alumina hydrate, a polishing accelerator and water, the alumina-type fine particles having an xcex1 conversion ratio of from 65 to 90% and a specific surface area of from 30 to 80 m2/g.
By the present invention, the polishing work can be favored with a high polishing rate for a metal film, particularly a high selection ratio, and reduction in scratches on the polished surface.